1. Field of the Invention
The present disclosure relates to a pump, and specifically to a micro pump that uses electro-osmosis and that can be applied to micro-total analysis system (μ-TAS), fluid integrated circuit (fluid IC), and so forth.
2. Description of the Related Art
Micro pumps that use electro-osmosis are advantageous in being relatively simple in structure, being easily mountable into micro flow passages, and so forth. Therefore, the micro pumps are used in fields such as μ-TAS, Lab-on-a-chip, and fluid IC.
Under such circumstances, micro pumps that use induced-charge electro-osmosis (ICEO) have been drawing attention in recent years, because such micro pumps increases the flow rate of a liquid, can be driven on an AC voltage to suppress a chemical reaction occurring between an electrode and the liquid, and so forth.
U.S. Pat. No. 7,081,189 (hereinafter referred to as “Patent Document 1”) and M. Z. Bazant and T. M. Squires, Phys. Rev. Lett. 92, 066101 (2004) (hereinafter referred to as “Non-Patent Document 1”) disclose pumps that use induced-charge electro-osmosis and that are configured as described in (1) or (2) below:    (1) a pump in which a half of a metal post placed between electrodes is coated with a dielectric thin film to control a region in which an electric charge is induced in the metal post by an electric field to control a liquid flow (an ICEO pump with a half-coated metal post); and    (2) a pump in which a metal post having an asymmetric shape such as a triangular shape is disposed between electrodes to control a liquid flow to a constant direction (an ICEO pump with an asymmetric metal post).
Applied Physics Letters 89, 143508 (2006) (hereinafter referred to as “Non-Patent Document 2”) discloses an AC-driven electro-osmosis pump (ACEO pump) in which rectangular electrodes with different electrode areas are provided opposite to each other in the direction in which a fluid flows through a flow passage and in which an AC voltage is applied between the rectangular electrodes to generate a pumping action. The AC-driven electro-osmosis pump is formed as a three-dimensional (3D) ACEO pump in which the rectangular electrodes are partially provided with a three-dimensionally stepped structure to improve the pumping performance.
Journal Applied Physics 96, 1730 (2004) (hereinafter referred to as “Non-Patent Document 3”) discloses a micro pump (planar-orthogonal micro-pump) which utilizes an electrokinetic phenomenon and in which a pair of linear thin-film electrodes are disposed perpendicularly to each other so as not to intersect each other.
The pumps which utilize electro-osmosis according to Patent Document 1 and Non-Patent Documents 1 to 3 are expected for their future utilization, but may not be able to demonstrate their full pumping performance if the flow passage is long, because the pump generates a relatively low pressure per unit area in the flow passage occupied by the pump. Increasing the length of the pump to enhance the generated pressure may increase the proportion of the area in the fluid integrated circuit occupied by the pump to increase the size and cost of the entire system.
Currently, pumps with a large size that require an external pressure generation source are generally used. If alternative pumps with a small size and a simple structure that do not require an external pressure source or the like can be provided, however, such pumps may drastically reduce the size and cost of the entire system, and may significantly widen the range of use of fluid integrated circuits.
If pumps with a small size and a simple structure that can demonstrate its full pumping performance even in the case where the flow passage is long can be provided, such pumps may achieve a fluid integrated circuit that not only allows control of a local flow but also allows integrated dynamic control of a macroscopic flow including liquid delivery in the entire fluid apparatus such as μ-TAS.
Patent Document 1 and Non-Patent Document 1 describes a fluid device that utilizes a sidewall flow due to an induced-charge electro-osmosis phenomenon of a conductive post disposed between electrodes. However, one end of the conductive post is not connected to the electrodes, and therefore a forward flow and a backward flow may be produced along the flow passage at the same time, which may reduce the pumping performance.
Non-Patent Document 2 describes a pump which utilizes ACEO and in which rectangular electrodes are partially provided with a three-dimensionally stepped structure. However, the pump is the same as ACEO pumps according to the related art in that it utilizes a flow on the top surface of the three-dimensionally stepped electrodes, and Non-Patent Document 2 does not describe or suggest utilizing a sidewall flow.
Non-Patent Document 3 describes a micro pump in which a pair of linear thin-film electrodes are disposed perpendicularly to each other so as not to intersect each other. However, the micro pump utilizes an electrokinetic phenomenon on the top surface of the thin-film electrodes, and Non-Patent Document 3 does not describe or suggest utilizing a sidewall flow.